The average structural evolution of massive galaxies can be reliably estimated using cumulative galaxy number densities [GA]

Galaxy evolution can be studied observationally by linking typical progenitor and descendant galaxies through an evolving cumulative number density selection. This selection can be made to reproduce the expected evolution of the median stellar mass from abundance matching. However, models predict an increasing scatter in main progenitor masses at higher redshifts, which makes galaxy selection at the median mass unrepresentative. Consequently, there is no guarantee that the evolution of other galaxy properties, deduced from this galaxy selection, are reliable. Despite this concern, we show that when we apply this selection to the EAGLE hydrodynamical simulation it approximately reproduces the evolution of the average stellar density profile of main progenitors of M = 10^11.5 Msun galaxies out to z = 5. The accuracy improves when we include the expected scatter in cumulative number densities. Our results suggest that cumulative number density matching can be expected to give reasonably accurate results when applied to the evolution of the mean density profile of massive galaxies. Moreover, the average density profile evolution in EAGLE broadly agrees with observations from UltraVISTA and CANDELS, suggesting an inside-out growth history for these massive galaxies over 0 < z < 5. However, for z < 2 the inside-out growth trend in EAGLE is stronger than suggested by these observations.